"Denied" or "cryptic" pregnancies occur often enough that they spawned their own television series (TLC's I Didn't Know I Was Pregnant), and the occasional example that makes the news always sets off a flurry of interest.
Yet for most of us, the idea that a woman could carry a child to a full-term delivery without knowing she is pregnant is mind-boggling, considering the changes her body goes through over 40 weeks. It has to be denial, or worse, right?
Fortunately there is some academic research on the topic. The numbers tossed around on the Internet (and the presence of an actual television series) can make this seem quite common.
The best statistic we seem to have comes from a German study of births at all Berlin metropolitan area hospitals back in 1995 and 1996. It showed that one in 475 women didn't know she was pregnant at 20 weeks, and one in 2455 gave birth to a viable foetus without realising she was pregnant until she went into labour.
The overall numbers are quite small - 62 for first group, and just 12 for the second - but they are enough to lead the authors to conclude that "the common view that denied pregnancies are exotic and rare events is not valid. Deliveries in which the woman has not been aware of her pregnancy until going into labour occur about three times more often than triplets". A couple of other studies came up with similar numbers for 20 weeks of gestation.
But, really, what we want to know is whether these women have serious psychological issues - or could something else be going on?
Last week in Boston, for example, Katherine Kropas discovered she was pregnant an hour before her daughter was delivered. The 23-year-old woman was using birth control, had a menstrual cycle and generally felt fine in the months before delivery. She had no morning sickness and her feet were only slightly swollen, which she attributed to being on them almost constantly in her catering job over the holidays.
At least two researchers have done literature reviews and come up with vastly different conclusions. In a 2011 study published in the Journal of the Royal Society of Medicine, one team found that such mothers have serious psychological problems. Dividing the "illness" into "psychotic" and "non-psychotic" varieties, the researchers wrote that "this inappropriate [defence] mechanism may be so powerful that the woman is genuinely unaware of her condition".
Such women are "unprepared for delivery and motherhood," they wrote, posing "significant risks for both the mother and foetus, including emotional disturbance, lack of antenatal care, precipitous delivery (often into the toilet bowl) and neonaticide". Any woman who denies her pregnancy for these lengths of time should be referred for psychiatric assessment, they argue.
But a 2006 review in the journal Medical Hypotheses offers a much more benign interpretation, even suggesting that these events be called "cryptic" pregnancies, instead of "denied" pregnancies.
Marco Del Giudice, now at the University of New Mexico, notes that there is conflicting information about whether the women suffered from psychological distress; that only 26 per cent of women completely stopped menstruating (some, in their 40s, mistook that for the onset of menopause); only 26 per cent reported nausea early in their pregnancies; and 56 per cent gained very little or no weight over the course of their pregnancies.
It may be that women who are unaware they are pregnant have suffered a number of early spontaneous abortions and have lower levels of a pregnancy hormone that causes such symptoms. Or being unaware that she is pregnant could be seen as an "adaptive emergency mechanism" for a woman facing the psychosocial stress of a partner who has deserted her or social isolation, he wrote.
"In my opinion, the literature on this condition is biased by a pervasive assumption that psychological denial is taking place, but, in the majority of cases, there is virtually no evidence supporting this assumption," Del Giudice said in an email.
"I've heard these stories over and over. You hear them and think, 'Oh my God, how did somebody not know'," Kropas' mother told NECN. "But I can tell you, this is real and true and it happens."